The New York Times - August 17, 2005
Dean E. Murphy

A study has found that new H.I.V. infections in San Francisco are fewer than local health officials thought.

Why do you think there has been a significant decline in new H.I.V. infections among gay men in San Francisco? Peter DaSilva for The New York Times

But the gathering last week at a coffee shop in the largely gay Castro district here was not a casual pickup session. The dozen or so men were infected with the virus that causes AIDS, and the talk was of "responsible sex," not through condoms, necessarily, but through choosing sex partners who are already infected.

"I don't think I could sleep at night if I knew I had infected another human being," said one of the men, Don Stewart, who tested positive for the virus, H.I.V., five years ago.

The monthly social event, called Positive Space and organized by an AIDS prevention group, is among the scores of educational meetings, workshops, seminars and parties that health officials here say may be contributing to a significant decline in the incidence of H.I.V. among gay men in San Francisco.

The national Centers for Disease Control and Prevention estimated in a report in June that new infections in San Francisco among men who have sex with men were occurring at about half the rate previously calculated by city health officials - 1.2 percent a year instead of 2.2 percent. That is the lowest rate reported in San Francisco since 1997 and the lowest among five cities with significant gay populations studied by the disease control agency.

Since the report's release, health officials here, known for their cautious approach to shifts in AIDS trends, have been scrambling to confirm the results and offer an explanation. Some officials have said that the decline has been fueled by conventional efforts like stepped-up H.I.V. treatment programs, easier and more regular tests, and so-called harm-reduction strategies like discouraging the use of crystal methamphetamine, a drug blamed for helping to spread the disease by lowering inhibitions.

But other signs, like the proliferation of matchmaking Web sites for men infected with H.I.V. and the relatively high number of men here who know their H.I.V. status, point to a growth in the number of men looking for partners with the same status. The practice is known as sero-sorting, which involves men choosing sex partners based on their common serostatus, a term that refers to the presence of antibodies to a particular infectious agent in the blood.

"Studies have shown when people have knowledge of their sero-status, they take that knowledge and use it to protect their partners," said Dr. Patrick S. Sullivan, chief of the behavioral and clinical surveillance branch at the disease control centers. "Sero-sorting is one piece of that whole benefit that arises from people learning their status through H.I.V. testing."

Since the AIDS epidemic began nearly 25 years ago, San Francisco has often been a laboratory of sorts, with many behavioral changes, both good and bad, occurring here before spreading to other cities.

Though the disease control centers' report is just one in a sea of statistical analyses and studies about H.I.V., containing the usual caveats about possible reporting errors and potentially skewed sampling, the emerging consensus in San Francisco is that the new numbers signal a reversal in a sharp rise in infections that began about seven years ago.

The highest incidence of new infection among men who have sex with men, 8 percent, was found in Baltimore, followed by Miami with 2.6 percent, New York with 2.3 percent and Los Angeles with 1.4 percent, according to the report's preliminary estimates, which were based on H.I.V. tests conducted among 1,767 men from June 2004 to April 2005.

"When I first saw the data, I was skeptical and had to be convinced," said Jeff Sheehy, an adviser on AIDS issues to Mayor Gavin Newsom of San Francisco. "There's a lot of fortunate events coming together to drive this. It's incredibly important to start people really looking at the factors driving the downward trend and reinforce and encourage those factors."

The federal report did not delve into possible causes, and there is no specific evidence to support any definitive conclusion. Dr. Sullivan said that the report was a "snapshot in time," and that there would not be directly comparable data available until another survey was conducted in 2007.

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Carol Pogash contributed reporting for this article.

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